Experimental and predictive approach for volcanic ash geopolymer in the stabilisation of expansive subgrade

This study investigated the stabilisation of expansive subgrades with volcanic ash (VA) geopolymer through a series of experimental tests, including unconfined compressive strength (UCS), water absorption, swelling potential, along with SEM and EDX analyses. The performance of the soil specimens was then evaluated in comparison with the road subgrade material requirements and ordinary Portland cement (OPC). Moreover, a new predictive model was developed using gene expression programming (GEP) to estimate the UCS values. The results revealed that VA geopolymer-stabilised specimens exhibited superior mechanical performance compared to those improved with OPC. A considerable decrease of approximately 98% in swelling and 95% in water absorption was detected with stabilisation. Microstructural analysis showed a denser and more compact soil matrix with VA incorporation. VA geopolymer stabilisation minimised CO2-e emissions by approximately 44% in comparison with OPC. Additionally, the GEP-based prediction model exhibited superior performance in the prediction of UCS values with low error. A multi-factor analysis of variance (ANOVA) was also carried out, and Pearson correlation coefficients were constructed to statistically evaluate the experimental results. The results revealed that the bulk density, swelling, water absorption and UCS parameters were predominantly affected by the molarity and curing duration.